Accretion dynamics and coronal geometry in Mrk 530: Insights from 24 years of X-ray monitoring

TL;DR

This 24-year study of Mrk 530 reveals stable long-term X-ray properties with episodic quasi-periodic oscillations linked to accretion rate changes, providing insights into accretion and coronal dynamics in active galactic nuclei.

Contribution

The paper offers the first long-term broadband analysis of Mrk 530, linking spectral evolution and variability to accretion rate changes and coronal geometry.

Findings

Detection of a possible quasi-periodic oscillation in 2018

Long-term evolution of spectral properties and soft excess

Correlation between accretion rate, spectral slope, and coronal size

Abstract

We present a long-term broadband study of the Seyfert galaxy Mrk~530 spanning $\sim$24 yr (2001--2024). The source remains largely stable across epochs, except in 2018, when a possible quasi-periodic oscillation is observed simultaneously in the UV and X-ray bands, with characteristic timescales of $\sim$90 and $\sim$60 days, characterized by low coherence. Time-resolved spectral analysis shows that this epoch is characterized by comparable coronal cooling and compressional heating timescales, a condition conducive to oscillatory behavior in the inner accretion flow. Other epochs exhibit a clear mismatch between these timescales, and no such variability is observed. The X-ray spectral properties display significant long-term evolution. The photon index and luminosity vary systematically, while a soft excess is present only in early epochs (2001--2006) and weakens thereafter, consistent with an evolving warm corona. Physically motivated models indicate that changes in the accretion rate regulate both the spectral slope and coronal geometry, with higher disc accretion rates producing enhanced cooling, a more compact corona, and softer spectra, and lower rates yielding an expanded hot flow and harder emission. These results suggest that accretion-driven coupling between the disc and corona governs both the long-term spectral evolution and transient short-timescale variability in Mrk~530.